Compositions – Vaporization – or expansion – refrigeration or heat or energy...
Reexamination Certificate
1998-07-23
2001-12-11
Einsmann, Margaret (Department: 1751)
Compositions
Vaporization, or expansion, refrigeration or heat or energy...
C510S408000, C510S412000, C570S177000, C570S178000, C570S180000
Reexamination Certificate
active
06328907
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an azeotropic mixture of 1,1,1,3,3-pentafluoropropane (which hereinafter may be referred to as also “R-245fa”) and hydrogen fluoride (which hereinafter may be referred to as also “HF”), and a process of separating/purifying R-245fa and/or hydrogen fluoride from a mixture comprising at least R-245fa and hydrogen fluoride.
BACKGROUND ART
R-245fa is a useful compound which can be used for an alternative for CFC (chlorofluorocarbon) or HCFC (hydrochlorofluorocarbon) used as a cooling medium and a foaming agent and which is not likely to destroy the ozone layer.
R-245fa can be produced by fluorination of 1,1,1,3,3-pentachloropropane using HF. In this production process, since an excessive amount of HF is used for the reaction, a reaction mixture contains a considerable amount of unreacted HF in addition to produced R-245fa, and also may contain, in addition to these, a by-product (for example, R-244fa (1,1,1,3-tetrafluoro-3-chloropropane) and so on). A composition of such a reaction mixture is determined by reaction conditions, and in order to obtain R-245fa from the reaction mixture as described above, the mixture is subjected to separation/purification. Further, it is desirable to recover the unreacted HF from the reaction mixture and re-used for the reaction.
In the present specification, the term “separate/purify” is intended to mean such that when a mixture stream comprising specific two components (for example, R-245fa and HF) is subjected to a certain processing step (for example, a distillation step) and thereby other stream is obtained in which stream a ratio of a concentration (a) of one specific component (for example, R-245fa) to a concentration (b) of the other specific component (for example, HF) of the stream (namely a ratio [a/b]) is increased, that is when the ratio [a/b] is increased to [a′/b′] (wherein a′/b′>a/b), the specific component (R-245fa) is said to be separated/purified.
Further, in the present specification, the term “separate/purify” is intended to not necessarily mean perfect separation, and such term is used to include a fairly broad meaning so that it includes a concept of so-called “concentration.” However, in one of the most preferable embodiments, the term “separate/purify” is intended to mean that a mixture stream consisting substantially of two specific components is subjected to a predetermined step so that other stream is obtained which contains substantially only one specific component. In another embodiment of the most preferable embodiments, the term “separate/purify” is intended to mean that a mixture stream consisting substantially of two specific components and at least one component is subjected to a predetermined step so that other stream is obtained which is substantially free from one of the specific components.
When R-245fa is separated/purified from a reaction mixture as described above, alkaline washing and/or water washing is usually used for the separation of unreacted HF from R-245fa (and other HFC if any). However, separated HF in such a manner is present in an aqueous solution and there is no other way than disposing it. Thus, the above mentioned separation not only wastes HF but also requires additional cost for washing and disposing. Therefore, it is desirable to provide a process of more effectively separating/purifying R-245fa and/or HF from a mixture of HF and R-245fa.
As to other HFCs such a s R-134a (1,1,1,2-tetrafluoroethane), there are examples in which using an azeotropic mixture of HF and the HFC, separating R-134a is separated from a mixture containing those compounds (see, for example, Japanese Patent Kokai Publication Nos. 4-261126 and 5-178768). However, with respect to the separation of R-245fa and/or HF from a mixture of R-245fa and HF, the presence of an azeotropic mixture of R-245fa and HF has not been known.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a process of separating/purifying R-245fa and/or HF from a mixture comprising at least R-245fa and HF without a washing step as described above.
The present inventors have intensively studied the process of separating/purifying R-245fa and/or HF from the mixture comprising at least R-245fa and HF, and have found for the first time that R-245fa and HF form a minimum azeotropic mixture and completed the present inventions.
Thus, the present invention provides an azeotropic mixture consisting substantially of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride. The azeotropic mixture is a minimum azeotropic mixture having a minimum boiling point. An azeotropic temperature and an azeotropic composition of the azeotropic mixture depend on a pressure of a system in which the azeotropic mixture is formed. Typical azeotropic temperatures and compositions are shown below which were measured in Example 2 which will be described below:
Pressure
Azeotropic
Azeotropic Composition
(kg/cm
2
-gauge)
Temperature (° C.)
(mol % of R-245fa)
2.95
40
34.5
3.50
45
40.8
4.20
50
45.0
5.80
60
48.2
7.00
67
48.5
7.65
70
47.4
9.00
77
42.1
9.60
80
36.3
The above azeotropic mixture has been found for the first time by the present inventors.
The azeotropic mixture can be used as reflux of a distillation step in which R-245fa or HF is separated/purified from a mixture comprising R-245fa and HF. In the distillation step, the mixture containing R-245fa and HF at any ratio of R245fa/HF is supplied to the distilling step as a feed, and R-245fa and HF are distilled off from the distilling step as an azeotropic mixture and a bottom product is obtained which has a higher or lower R-245fa/HF ratio, then that of the feed depending on the R245fa/HF ratio of the feed, whereby effective separation/purification of R-245fa or HF is possible.
That is, the present invention provides a process of separating/purifying 1,1,1,3,3-pentafluoropropane or hydrogen fluoride in which a mixture comprising at least 1,1,1,3,3-pentafluoropropane and hydrogen fluoride as a feed is subjected to a distillation step so that a distillate is obtained which comprises an azeotropic mixture consisting substantially of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride and a bottom product is obtained which comprises separated/purified 1,1,1,3,3-pentafluoropropane or hydrogen fluoride.
The feed which can be used in the present process comprises at least R-245fa and HF, and in a preferred embodiment, the feed consists substantially of R-245fa and HF. In the latter embodiment, the azeotropic mixture is substantially distilled off and R-245fa which contains substantially no HF or HF which contains substantially no R-245fa is obtained as a bottom product. Optionally, the feed may contain other component such as 1,1,1,3,3-pentachloropropane, 1,1,1,3-tetraluoro-3-chloropropane and so on. Such other component(s) is merely distributed to the distillate or the bottom product depending on its boiling point at an operation pressure of the distillation step and an azeotropic temperature of the other component and HF if they form another azeotropic mixture. As a concrete example, the feed may be a reaction mixture obtained upon the production of R-245fa from pentachloropropane and HF.
When a ratio of R-245fa/HF of the feed is smaller than that of an azeotropic mixture which is formed at an operation pressure of the distillation step, a distillation bottom product comprising HF which is substantially free from R-245fa (or which contains substantially no R-245fa) is obtained by a distillation operation in which a distillate comprising an azeotropic mixture of R-245fa and HF is obtained, and a portion of the distillate is used as reflux.
To the contrary, when the ratio of R-245fa/HF of the feed is larger than that of the azeotropic mixture which is formed at the operation pressure of the distillation step, a distillation bottom product which is substantially free from HF (or which contains substantially no HF) is obtained by a distillation operation in which the distillate comprising the azeotropic mixture
Nakada Tatsuo
Shibanuma Takashi
Shibata Noriaki
Birch & Stewart Kolasch & Birch, LLP
Daikin Industries Ltd.
Einsmann Margaret
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